Synchrotron-radiated X-ray and neutron diffraction study of native cellulose

Precise determination of d-spacings and compositional ratio of cellulose I_α and I_β in various native cellulose samples was successfully carried out by synchrotron-radiated X-ray diffraction and time-of-flight (TOF) neutron diffraction from quasi-powder specimens. X-ray diffraction peaks were separated by the deconvolution method using six types of profile function: Gaussian, Lorentzian, intermediate Lorentzian, modified Lorentzian, pseudo-Voigt, and Pearson VII. In terms of R-factors, the pseudo-Voigt function gave the best fit with the observation, and was used for determination of d-spacings. The numerical results for Valonia cellulose were: dI_α (1 0 0) = 0.613 nm; dI_β (1 1 0) = 0.603 nm; dI_β (1 1 0) = 0.535 nm; dI_α (0 1 0) = 0.529 nm; I_α content = 0.65. The differences determined between dI_α (1 0 0) and dI_β (1 1 0) and between dI_β (1 1 0) and dI_α (0 1 0) were similar to those previously reported. Comparison between unresolved peaks for the two types of cellulose samples revealed a small but definite difference between dI_α (1 1 0) and dI_β (2 0 0). The TOF neutron diffractometry using deuterated samples confirmed this difference. This revised version was published online in August 2006 with corrections to the Cover Date.     

Size,shape, orientation and crystallinity of cellulose I<Subscript>β</Subscript> by X-ray powder diffraction using a free spreadsheet program

X-ray powder diffraction is one of the most commonly used methods in cellulose science. This technique is used to identify the cellulose allomorphs, their crystallinity, and the size of their crystallites. In this paper, a novel model is introduced that implicitly takes into account the shape and size of cellulose I_β crystallites in the interpretation of powder diffractograms. Because of the limited amount of data in cellulose powder patterns, this model focuses on a small number of adjustable parameters. The method hypothesizes that cellulose I_β crystallites are straight crystalline rods with superelliptical cross-sections. This superellipse is a parametric curve that can, for example, describe various crystallite shapes as rectangles or ellipses. Additionally, preferred orientation along the (0 0 1) crystallographic planes can be modelled using the March–Dollase approach. The simulated background has a semi-empirical form. An initial model comprised cellulose I_β crystallites and the amorphous background. A second model comprised a biphasic distribution of crystallites and the same amorphous background. In this second model, large cellulose I_β crystallites coexisted with more slender crystallites, usually less than 20 Å in lateral size. Cellulose IV_I nanocrystals were selected as a modeling construct to represent these small and distorted forms of native cellulose. Both models produced simulations in excellent agreement with the experimental measurements.     

Young’s modulus calculations for cellulose I<Subscript>β</Subscript> by MM3 and quantum mechanics

Quantum mechanics (QM) and molecular mechanics (MM) calculations were performed to elucidate Young’s moduli for a series of cellulose I_β models. Computations using the second generation empirical force field MM3 with a disaccharide cellulose model, 1,4′-O-dimethyl-β-cellobioside (DMCB), and an analogue, 2,3,6,2′,3′,6′-hexadeoxy-1,4′-O-dimethyl-β-cellobioside (DODMCB), that cannot make hydrogen bonds reveal a considerable contribution of intramolecular hydrogen bonding to the molecular stiffness of cellulose I_β; the moduli for DMCB and DODMCB being 85.2 and 37.6 GPa, respectively. QM calculations confirm this contribution with modulus values of 99.7 GPa for DMCB and 33.0 GPa for DODMCB. However, modulus values for DMCB were considerably lower than values previously reported for cellulose I_β. MM calculations with extended cellulose chains (10–40 glucose units) resulted in modulus values, 126.0–147.5 GPa, more akin to the values reported for cellulose I_β. Comparison of the cellodecaose model, 1,4′-O-dimethyl-β-cellodecaoside (DMCD), modulus with that of its hydrogen bonding-deficient analogue, 2,3,6,2′,3′,6′-hexadeoxy-1,4′-O-dimethyl-β-cellodecaoside (DODMCD), corroborates the observed stiffness conferred by intramolecular hydrogen bonds; the moduli for DMCD and DODMCD being 126.0 and 63.3 GPa, respectively. Additional MM3 determinations revealed that modulus values were not strongly affected by intermolecular hydrogen bonding, with multiple strand models providing values similar to the single strand models; 87.5 GPa for a 7-strand DMCB model and 129.5 GPa for a 7 strand DMCD model.     

Hydrothermal synthesis and crystal structure of [Ni(Bptc)<Subscript>2</Subscript>(Bimb)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>]

In the compound [Ni(Bptc)₂(Bimb)₂(H₂O)₂] (I), where H₄Bptc is 3,3′,4,4′-biphenyltetracarboxylic acid; Bimb is 4,4′-bis(1-imidazolyl)biphenyl), Ni(II) has a distorted octahedral coordination geometry, which was bonded with two N atoms from two Bimb ligands, two O atoms from two H₂Bptc²⁻ ligands and two water O atoms. The crystal structure of compound I is stabilized by the π-π-stacking and hydrogen bonds interaction.     

Conductivity of SnO<Subscript>2</Subscript>-In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystalline composite films

The conductivity of films consisting of a mixture of SnO₂ and In₂O₃ nanocrystals at 200–500°C was studied. Based on the experimental data, it was assumed that in films containing less than 20 wt % In₂O₃, the current flows along SnO₂ nanocrystals. A model of conductivity in these films is presented; it includes an electron transfer from In₂O₃ to SnO₂, which forms positively charged In₂O₃ nanocrystals that contact the negatively charged SnO₂ nanocrystals. In the presence of In₂O₃ nanocrystals, the activation energy of the electron transfer between SnO₂ nanocrystals decreased substantially because of a decrease in the barrier of electron transfer between SnO₂ crystals under the action of the negative charge. As a result, a percolation cluster of charged SnO₂ crystals formed. At high contents of In₂O₃ (over 20 wt %), the conductivity increased dramatically. The curve of the temperature dependence of conductivity changed because of the appearance of a percolation cluster of In₂O₃ nanocrystals, in which the current passed. The conductivity of a mixed film of this kind differed from that of the nanocrystalline film of pure In₂O₃.     

Reactivity of C<Subscript>3</Subscript>-C<Subscript>8</Subscript> alkanes with nitronium ions in sulfuric acid

We have determined the parameters of the Arrhenius equation (E, log A) for reactions between \textNO₂⁺ {\text{NO}}_2^{+} ions and C₃-C₈ alkanes in HNO₃–93 wt.% H₂SO₄ solutions at 277–353 K, and we have also estimated the activation parameters E _j , log A _j for secondary and tertiary C—H bonds of these alkanes. We show that the following compensation relations are satisfied: E = 2.3R βlog A + C with isokinetic temperature β = 360 ± 65 K, and also E _j =2.3Rβ _j log A _j  + C _j , for secondary C—H bonds, β₂ =300 ± 60, and for tertiary C—H bonds, β₃ =310 ± 50.     

New metal-rich mixed chalcogenides with an intergrowth structure: Ni<Subscript>5.68</Subscript>SiSe<Subscript>2</Subscript>, Ni<Subscript>5.46</Subscript>GeSe<Subscript>2</Subscript>, and Ni<Subscript>5.42</Subscript>GeTe<Subscript>2</Subscript>

New metal-rich mixed nickel-silicon and nickel-germanium chalcogenides, Ni_5.68SiSe₂, Ni_5.46GeSe₂, and Ni_5.42GeTe₂, were synthesized by high-temperature ceramic techniques. The X-ray diffraction study of single crystals grown from a molten flux revealed that the compounds are isostructural and crystallize in the tetragonal system (space group I4/mmm, Z = 2). These compounds are the first members of the family of M_7−δEX₂-type (M = Ni or Pd; E = Sn or Sb; X is chalcogen) intergrowth structures containing “light” p elements E. Resistivity measurements on pressed textured pellets showed that both selenides are anisotropic metallic conductors in the directions parallel and perpendicular to the heterometallic bond systems. The geometric criteria of stability of the intergrowth structure type under consideration are discussed. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1632–1638, September, 2007.     

Crystalline forms of cellulose in the silver tree fern Cyathea dealbata

Solid-state ¹³C NMR spectroscopy was used to characterize fibrous material cut from the midrib of a fern frond. Signals associated with cellulose crystallites were separated from those associated with the lignin--hemicellulosic matrix by exploiting differences in proton rotating-frame relaxation time constants. Heights of signals at 90.2 and 88.5 ppm, assigned to C-4 in cellulose I_α and I_β, indicated similar proportions of the two crystalline forms. This observation conflicts with a suggestion that plant celluloses can be grouped into the two categories of I_α-rich and I_β-rich. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase relations in the Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>-Cu<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> system from room temperature to melting

Phase relations in the Zn₂V₂O₇-Cu₂V₂O₇ system were studied by high-temperature X-ray diffraction and differential thermal analysis. The major phase constituents of the system are solid solutions based on Zn₂V₂O₇ and Cu₂V₂O₇ polymorphs and their coexistence regions. The generation of α-Zn_{2 − 2x} Cu_2x V₂O₇ solid solution, where 0 ≤ x ≤ 0.30, leaves almost unchanged the stabilization temperature of the high-temperature zinc pyrovanadate phase. The α-Cu_{2 − 2x} Zn_2x V₂O₇ homogeneity range is 5 mol % Zn₂V₂O₇. In the range 0.050 ≤ x ≤ 0.09 from 20 to ∼ 620°C, there is the two-phase field of α-Cu₂V₂O₇ and β-Cu₂V₂O₇ base solid solutions. At still higher temperatures, β-Zn_{2 − 2x} Cu_2x V₂O₇ and α-Cu_{2 − 2x} Zn_2x V₂O₇ coexist in the mixed-phase region. β-Zn_{2 − 2x} Cu_2x V₂O₇ solid solution, where 0 ≤ x ≤ 0.30, exists above 610 ± 5°C. The extent of the β′-Cu₂V₂O₇-base solid solution is 9 to 65 mol % Zn₂V₂O₇ at 615 ± 5°C, expanding to 0 mol % Zn₂V₂O₇ with rising temperature. Original Russian Text ￠ T.I. Krasnenko, M.V. Rotermel’, S.A. Petrova, R.G. Zakharov, O.V. Sivtsova, A.N. Chvanova, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 10, pp. 1755–1762.     

Synthesis and spectroscopic characteristics of σ-vinyl derivatives of platinum(<Emphasis Type="SmallCaps">IV</Emphasis>) chloride complexes

A procedure was developed for the synthesis of previously unknown β-chlorovinyl derivatives of Pt^IV chloride complexes by chloroplatination of terminal alkynes catalyzed by Pt^II chloride complexes. The reaction is highly stereoselective and gives only the products of trans-anti-addition of platinum and chlorine atoms. The regioselectivity of the catalytic reaction formally corresponds to Markovnikov’s rule, e.g., in alkynes containing electron-donating substituents, platinum attacks the terminal carbon atom. The σ-vinyl derivatives of Pt^IV chloride complexes were characterized by IR spectroscopy and ¹H and ¹³C NMR spectroscopy. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2380–2384, October, 2005.     

The phase diagram of V<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript>-Ag<Subscript>2</Subscript>O system

The results concerning the synthesis, structure and thermal properties of V₂O₅-MoO₃-Ag₂O samples in the molybdenum rich region of ternary system are presented in the form of quasi-binary systems: β-AgVO₃-β-Ag₂MoO₄, AgVMoO₆-MoO₃, AgVMoO₆-Ag₂Mo₄O₁₃, AgVMoO₆-Ag₂Mo₂O₇, AgVMoO₆-β-Ag₂MoO₄ and also of the system in which at V₂O₅/MoO₃ molar ratio 3:7 the content of Ag₂O was variable. The ternary phase AgVMoO₆ was not described earlier in the literature.     

Thermodynamic study of glasses in Ag-As-Se system using EMF method with Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript> solid electrolyte

The EMF method with Ag₄RbI₅ solid electrolyte was used to study silver solubility in Ag-As-Se glasses on the basis of the cross-sections of (I) Ag-As_0.25Se_0.75, (II) Ag-As_0.33Se_0.67, (III) Ag-As_0.4Se_0.6, and (IV) Ag-As_0.5Se_0.5. It is found that silver solubility reaches 30 and 40 at % in sections (I), (IV) and (II), (III), accordingly. The data of EMF measurements were used as a basis for calculation of partial polar functions of Ag in glasses. The Gibbs-Duhem equations were integrated to calculate thermodynamic functions of silver dissolution in vitreous As _x Se_{1 − x} (x = 0.25; 0.33; 0.4; 0.5), from which the corresponding data for the latter were used to obtain the standard integral thermodynamic functions of the mixing of glasses. The obtained results were compared with the thermodynamic data for crystalline silver selenoarsenites.     

Whitlockite solid solutions in the Ca<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>-K<Subscript>3</Subscript>VO<Subscript>4</Subscript>-NdVO<Subscript>4</Subscript> system

Phase equilibria in the Ca₃(VO₄)₂-K₃VO₄-NdVO₄ system have been studied. An extensive calcium orthovanadate-based solid solution was found to form with the boundary compositions as follows: Ca₃(VO₄)₂-Ca₉Nd(VO₄)₇-Ca_9.33K_2.33(VO₄)₇-Ca_7.88K_2.63Nd_0.87(VO₄)₇. The unit cell parameters of the whit-lockite vanadates synthesized increase as the potassium and neodymium contents increase. Phase transitions from the low-temperature β phase to the β′ centrosymmetrical structure in Ca_{9.33 − 5z} K_{2.33 + z} Nd_3z (VO₄)₇ vanadates have been studied dilatometrically. The increase in the β ai β′ transition temperature caused by potassium is interpreted as arising from the filling in of vacant cation positions M(4) and M(6).     

Silicate complexation of NpO<Subscript>2</Subscript><Superscript>+</Superscript> ion in perchlorate media

Complexation behavior of NpO₂ ⁺ with ortho-silicic acid (o-SA) has been studied using solvent extraction at ionic strengths varying from 0.10 to 1.00M (NaClO₄) at pcH 3.68±0.08 and 25 °C with bis-(2-ethylhexyl) phosphoric acid (HDEHP) as the extractant. The stability constant value (log β₁) for the 1:1 complex, NpO₂(OSi(OH)₃), was found to decrease with increase in ionic strength of the aqueous phase [6.83±0.01 at I=0.10M to 6.51±0.02 at I = 1.00M]. These values have been fitted in the SIT model expression and compared with similar values of complexation of the metal ions Am³⁺, Eu³⁺, UO₂ ²⁺, PuO₂ ²⁺, Np⁴⁺, Ni²⁺ and Co²⁺. The speciation of NpO₂ ⁺-o-silicate/carbonate system has been calculated as a function of pcH under ground water conditions. On leave from Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India.     

Liquid-solid metastable phase equilibria for the quaternary system (NaCl-KCl-CaCl<Subscript>2</Subscript>-H<Subscript>2</Subscript>O) at 308.15 K

The solubility and the physicochemical properties (densities, viscosities, refractive indices, conductivities and pH) in the liquid-solid metastable system (NaCl-KCl-CaCl₂-H₂O) at 308.15 K have been investigated using the isothermal evaporation method, and the dry-salt phase diagram, water-phase diagram, and the diagram of physicochemical properties vs. composition in the system were plotted. One three-salt cosaturated point, three metastable solubility isotherm curves, and three crystallization regions corresponding to sodium chloride, potassium chloride and calcium chloride tetrahydrate were formed, and neither solid solution nor double salts were found. On the basis of the extended Harvie-Weare (HW) model and its temperature-dependent equation, the values of the Pitzer parameters β⁽⁰⁾, β⁽¹⁾, C ^ϕ for NaCl, KCl and CaCl₂, the mixing ion-interaction parameters θ_Na,K, θ_Na,Ca, θ_K,Ca, Ψ_Na,K,Cl, Ψ_Na,Ca,Cl, Ψ_K,Ca,Cl, and the Debye-Hückel parameter A ^ϕ and the chemical potentials of the minerals in the quaternary system at 308.15 K were fitted, and the predictive solubility based on the temperature-dependent equation and the chemical potentials of the minerals agrees well with the experimental data.     

Hydrolysis behavior of various crystalline celluloses treated by cellulase of Tricoderma viride

Cellobiose and glucose are valuable products that can be obtained from enzymatic hydrolysis of cellulose. This study discusses changes in the crystalline form of celluloses to enhance the production of sugars and examines the effect on structural properties during enzymatic hydrolysis. Various crystalline celluloses consisting of group I (cell I, cell III_I, cell IV_I) and group II (cell II, cell III_II, cell IV_II) of similar DPs were prepared as starting materials. The similar DP values allowed a more direct comparison of the hydrolysis yields. The outcomes were analyzed and evaluated based on the residues and supernatants obtained from the treatment. As a result: (1) action of the cellulase of Trichoderma viride decreased both DP and crystallinity, with greater changes in group II celluloses, (2) the polymorphic interconversion process that occurred for cell III_I, cell IV_I, cell III_II and cell IV_II during the treatment was independent of the enzymatic hydrolysis, thus, the hydrolysis behaviors depended on the starting material of the celluloses, and (3) higher sugar production was obtained from cell III_I and group II. Therefore, the hydrolysis behavior of the various crystalline celluloses depended on the particular polymorph of the starting material.     

MoS<Subscript>2</Subscript> single slab as a model for active component of hydrodesulfuration catalyst: a quantum chemical study 1. Molecular and electronic structure of Mo<Subscript>12</Subscript>S<Subscript>24</Subscript> macromolecule and its adsorption complex with H<Subscript>2</Subscript>S

The molecular and electronic structure of Mo₁₂S₂₄ macromolecule as the MoS₂ single slab structure was calculated by the density functional theory (DFT) method with the B3P86 hybrid exchange-correlation functional. The results of calculations point to slight relaxation of coordinatively unsaturated Mo and S atoms, which is consistent with the published data. The calculated width of the forbidden band (0.85–0.98 eV) is comparable with the experimental value (1.30 eV) and similar to that obtained from DFT calculations with periodic boundary conditions (0.89 eV). The surface Mo centers in the Mo₁₂S₂₄ macromolecule are more reduced than the internal (Mo^IV) atoms. In order to characterize the adsorption capacity of coordinatively unsaturated Mo centers, a Mo₁₂S₂₄·6H₂S adsorption complex was calculated. The structure and energy characteristics of the adsorption complex point to a weak donor-acceptor interaction of the π-lone pair of H₂S molecule with the surface (reduced) Mo centers. The active center of thiophene hydrodesulfuration catalysts is formed as a result of the oxidative addition of hydrogen followed by occlusion of hydrogen into the MoS₂ matrix. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2189–2193, October, 2005.     

The synthesis and selected properties of Co<Subscript>2</Subscript>InV<Subscript>3</Subscript>O<Subscript>11</Subscript>

It has been demonstrated that Co₂V₂O₇ and InVO₄ react with each other forming a new compound of the Co₂InV₃O₁₁ formula, when their molar ratio is equal to 1:1, or among CoCO₃, In₂O₃ and V₂O₅, mixed at a molar ratio of 4:1:3. This compound melts incongruently at the temperature of 960±5°C, depositing crystals of InVO₄. It crystallizes in the triclinic system and the unit cell parameters amount to: a=0.6524(6) nm, b=0.6885(5) nm, c=1.0290(4) nm, α=96.5°, β=104.1°, γ=100.9°, Z=2. The phase equilibria being established in the Co₂V₂O₇–InVO₄ system over the whole components concentration range up to the solidus line were described.     

Structure and properties of H<Subscript>8</Subscript>(PW<Subscript>11</Subscript>TiO<Subscript>39</Subscript>)<Subscript>2</Subscript>O heteropoly acid

Heteropoly acid (HPA) H₈(PW₁₁TiO₃₉)₂O·xH₂O (I) is synthesized by three different ways and studied by chemical analysis, potentiometric titration, mass-spectrometry, IR, ³¹P, ¹⁸³W, and ¹⁷O NMR spectroscopy, thermogravimetry, and transmission electron microscopy. Anion I consists of two subparticles of the Keggin structure bridged by Ti-O-Ti. The dimeric anion exists in HPA aqueous solutions at [I] > 0.02 M. At pH > 0.6 it splits to a [PW₁₁TiO₄₀]⁵⁻ monomer stable up to pH ∼ 6. When heated (150–400)°C, I splits into H₃PW₁₂O₄₀ and, apparently, H₃PW₁₀Ti₂O₃₈ without phase separation. Thermolysis products are soluble and when dissolved in water turn again into I. Complete decomposition of I to oxides occurs at ∼450°C.     

Synthesis and crystal structure of new double mercury silver phosphide iodide Hg<Subscript>12</Subscript>Ag<Subscript>41</Subscript>P<Subscript>88</Subscript>I<Subscript>41</Subscript>

New double mercury silver phosphide iodide Hg₁₂Ag₄₁P₈₈I₄₁ (1) was synthesized and its crystal structure was established. Compound 1 crystallizes in the cubic system. The characteristic feature of the crystal structure 1 is the presence of the anionic cage clusters P₁₁ ³⁻, which have been previously found in alkali metal compounds only. The well-ordered P₁₁ ³⁻ clusters form a system of polyhedra, which encapsulate various disordered α-AgI-type fragments. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1882–1886, October, 2007.